Ministers have been forced to explain how they would guarantee the welfare of the 31,000 residents of the beleaguered Southern Cross care homes chain in the event of its collapse, as MPs on Tuesday queued up in parliament to express concern about the wellbeing of vulnerable people.

The Labour leader, Ed Miliband, seized on the twin scandals of Southern Cross's plight and the exposure by the BBC Panorama programme of abuse of people with learning disabilities at a private hospital near Bristol, calling for urgent government action on both fronts.

As Tory and Liberal Democrat backbenchers joined Labour in seeking assurances on the prospects for their elderly and disabled constituents, the care services minister, Paul Burstow, said there were plans for "decisive action" if Southern Cross went under and that he had not ruled out ordering a full inquiry into the Bristol affair.

Describing as "obscene" the abuse filmed secretly at the Winterbourne View hospital, operated by Castlebeck, Burstow said: "Nobody who watched the Panorama programme could have been anything but shocked and appalled by the systematic abuse of residents."

The crisis facing Southern Cross has led to fears that other firms in the sector are also "on the brink" of collapse, according to the union, Unison. It said problems facing Southern Cross may not be a one-off, claiming that other care home providers had financial difficulties. Miliband, who said he had been sickened by the scenes of abuse which "shame our country", demanded an independent investigation going beyond the reviews already begun by the Care Quality Commission, the care sector watchdog, and by South Gloucestershire council.

Terry Bryan, the whistleblower who tipped off Panorama about abuse at Winterbourne View, after failing to get a response from the CQC, is being brought in by the watchdog to advise it on one of its reviews. Bryan, who was a senior nurse at the hospital, will on Wednesday join experts in care of people with learning disabilities at a meeting called by the CQC to discuss how it should conduct a programme of urgent inspections of 150 similar units in the private sector and the NHS.

In an interview with Society Guardian, the CQC chair Dame Jo Williams said she had approached Bryan for his help after apologising that her organisation had failed to act on two separate emails he had sent, raising his concerns. He had been "extraordinarily reasonable and pleased to be asked".

Miliband also called on the government to consider the immediate extension of care regulation to include the financial stability of providers. Warning that "we cannot let Southern Cross happen again", Miliband said: "It is plain wrong that financiers creamed off millions, while as we now know the care of tens of thousands of elderly people was being put at risk."

Burstow said any decision on a full inquiry into Winterbourne View would be taken after the results of the CQC and South Gloucestershire reviews were known. He announced that Mark Goldring, chief executive of learning disability charity Mencap, would be giving independent advice on the findings.

On Southern Cross, the minister said that government officials had been, and remained in, close touch with the company and believed that its problems were "capable of resolution within the sector". However, contingency plans were in place should the company fail. "No resident – whether publicly or self-funded – would be left homeless or without care," Burstow said.

"In an emergency, a local authority can provide residential accommodation to anyone who has an urgent need for it. A local authority would continue to provide care for any self-funding resident who was unable to arrange care for themselves."

Williams, a former chief executive of Mencap, said that she had "of course" considered resigning her part-time, £60,000-a-year role over the affair, but had resolved to stay to lead the organisation's improvement.

Two further staff members at Winterbourne View have been arrested by police, bringing the total to six.